Conference Agenda

This research and collaboration project aims at improving confidence on the results produced by permanent satellite altimetry calibration and validation (Cal/Val) facilities in Europe and China: (1) the Permanent Facility for Altimetry Calibration established by ESA in Crete, Greece, and (2) the National Altimetry Calibration Cooperation Plan of China. This goal is accomplished by attaining the Fiducial Reference Measurements (FRM) strategy, established by the European Space Agency. Redundancy in scientific instrumentation, diversity of Cal/Val techniques, measurement traceability to SI units and uncertainty budget reporting are some of the requirements to achieve the FRM status.

European (i.e., Sentinel-6, Sentinel-3A/B) and Chinese (i.e., HY-2B/C/D) satellite altimetry missions are being calibrated and monitored using uniform, standardized procedures and protocols while exploiting trusted and indisputable reference standards at both Cal/Val infrastructures in Europe and China. These FRM-quality ground measurements could be certainly used to monitor the performance of other satellite altimetry missions (i.e., CryoSat-2, Guanlan, CRISTAL, etc.) as well.

Calibration of satellite altimeters has been accomplished by examining actual satellite observations in open seas against reference ground measurements defined by Cal/Val infrastructures at specific locations in Europe and China.

During this fourth year of this Dragon-5 collaboration, the following tasks are being carried out:

• Development of two new sea-surface Cal/Val sites in Crete, Greece;
• Absolute calibration of the HY-2B/C sea-surface height bias has been determined by European and Chinese Cal/Val infrastructures following diverse and independent methodologies;
• Independent and diverse techniques for estimating altimeter biases are applied by the European and Chinese teams;
• Uncertainties for the results of satellite calibration are reported in a realistic, universal and objective way;
• Final Cal/Val results are reported and intercompared at the two Cal/Val facilities.

The main findings of this joint work are:

• Both European and Chinese Cal/Val sites provide ground measurements of FRM-quality;
• Operations and data processing are standardized at both Cal/Val reference infrastructures in Europe and China;
• The performance of European and Chinese satellite altimeters is continuously monitored by the two Cal/Val infrastructures in China and Europe;

Sentinel-6, Sentinel-3A, Sentinel-3B, HY-2B and HY-2C meet the end-user requirements and expectations.

This presentation systematically presents the comprehensive outcomes of data processing, calibration, and validation efforts for key environmental variables measured by the Bufeng-1 (BF-1) mission, which has been operational in orbit since 2019. The presentation opens by offering an insightful introduction to the Global Navigation Satellite System Reflectometry (GNSS-R) technique. This is a cutting-edge method pivotal for the BF-1 mission's objective to capture and analyze Earth's reflected signals for global monitoring of sea surface winds, land surface soil moisture, and sea surface heights.

Following the introduction, we provide a detailed overview of the BF-1 mission, emphasizing its significance within the Chinese spaceborne observation portfolio and the specific data specifications employed in our research. This segment lays the groundwork for understanding the mission's unique contributions to Earth observation and the technical nuances involved in data acquisition and analysis.

The core of the presentation delves into the rigorous calibration and validation processes that underpin the BF-1 mission's operational success. By focusing on the production of delay Doppler maps (DDMs), we illustrate how these processes support the accurate and reliable observation of sea and land surfaces. The narrative then transitions to discussing the strategic role of the Chinese Beidou System (BDS) in the mission's Equivalent Isotropic Radiated Power (EIRP) acquisition program, a critical aspect for enhancing the precision of DDM observable production.

Moreover, we spotlight the novel results for deriving sea surface height (SSH) measurements and wind speed estimates with machine learning method (ML). These methodologies represent a significant advancement in the field, enabling more accurate, spatial-temporally aligned observations. The validation of these measurements employs auxiliary datasets, including the Denmark Technology University (DTU) mean sea surface (MSS) products and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis, ensuring a robust comparison and confirmation of the BF-1 data's accuracy and reliability.

In addition to presenting new findings, the presentation revisits previously published results on sea surface winds retrieval under hurricane conditions and soil moisture retrieval, further demonstrating the BF-1 mission's wide-ranging applications and its impact on environmental monitoring and disaster management.

The conclusion synthesizes the BF-1 derived results, discussing their implications for current and future works in the field. By highlighting the mission's contributions to advancing global environmental monitoring and its potential for supporting future research, the presentation underscores the BF-1 mission's role in enhancing our understanding of Earth's dynamic systems.